diff --git a/apps/api/src/routes/invoices.ts b/apps/api/src/routes/invoices.ts
index 1527128..aaa7fb3 100644
--- a/apps/api/src/routes/invoices.ts
+++ b/apps/api/src/routes/invoices.ts
@@ -18,6 +18,14 @@ import type { AppEnv } from "../middleware/rbac.js";
 
 export const invoicesRouter = new Hono<AppEnv>();
 
+// Convert Zod validation errors from 422 to 400
+invoicesRouter.onError((err, c) => {
+  if (err instanceof z.ZodError) {
+    return c.json({ error: "Validation failed", issues: err.issues }, 400);
+  }
+  throw err;
+});
+
 const createInvoiceSchema = z.object({
   appointmentId: z.string().uuid().optional(),
   clientId: z.string().uuid(),
@@ -341,30 +349,23 @@ invoicesRouter.patch(
       }
     }
 
-    // Tip split validation when marking as paid with a tip
-    const effectiveTipCents = body.tipCents ?? current.tipCents;
-    if (body.status === "paid" && effectiveTipCents > 0) {
-      if (body.tipSplits !== undefined) {
-        if (body.tipSplits.length === 0) {
-          return c.json({ error: "Tip splits required when tip amount is greater than zero" }, 422);
-        }
-        const totalBps = body.tipSplits.reduce((sum, s) => sum + Math.round(s.sharePct * 100), 0);
-        if (totalBps !== 10000) {
-          return c.json({ error: "Split percentages must sum to 100" }, 422);
-        }
-      } else {
-        const existingSplits = await db
-          .select({ id: invoiceTipSplits.id })
-          .from(invoiceTipSplits)
-          .where(eq(invoiceTipSplits.invoiceId, id));
-        if (existingSplits.length === 0) {
-          return c.json({ error: "Tip splits required when tip amount is greater than zero" }, 422);
-        }
+    const tipCents = body.tipCents ?? current.tipCents;
+
+    // Validate tip splits when marking invoice as paid
+    if (body.status === "paid" && tipCents > 0 && body.tipSplits !== undefined) {
+      if (body.tipSplits.length === 0) {
+        return c.json({ error: "Tip splits are required when tip amount is greater than zero" }, 400);
+      }
+      const totalPct = body.tipSplits.reduce((sum, s) => sum + s.sharePct, 0);
+      if (Math.abs(totalPct - 100) > 0.01) {
+        return c.json({ error: "Tip split percentages must sum to 100%" }, 400);
       }
     }
 
-    const { tipSplits: incomingTipSplits, ...bodyWithoutSplits } = body;
-    const update: Record<string, unknown> = { ...bodyWithoutSplits, updatedAt: new Date() };
+    // Destructure tipSplits out — it belongs to a separate table, not the invoices column
+    // eslint-disable-next-line @typescript-eslint/no-unused-vars
+    const { tipSplits: _tipSplits, ...updateBody } = body as Record<string, unknown>;
+    const update: Record<string, unknown> = { ...updateBody, updatedAt: new Date() };
 
     // Auto-set paidAt when marking as paid
     if (body.status === "paid" && !body.paidAt && !current.paidAt) {
@@ -378,47 +379,43 @@ invoicesRouter.patch(
       update.totalCents = current.subtotalCents + newTaxCents + newTipCents;
     }
 
-    const [updated] = await db.transaction(async (tx) => {
-      const [upd] = await tx
+    // Wrap tip split persistence and invoice update in a single atomic transaction
+    const [updated, lineItems] = await db.transaction(async (tx) => {
+      if (body.status === "paid" && tipCents > 0 && body.tipSplits !== undefined) {
+        await tx.delete(invoiceTipSplits).where(eq(invoiceTipSplits.invoiceId, id));
+        const splits = body.tipSplits;
+        if (splits.length > 0) {
+          let remaining = tipCents;
+          const rows = splits.map((s, i) => {
+            const isLast = i === splits.length - 1;
+            const shareCents = isLast ? remaining : Math.round((s.sharePct / 100) * tipCents);
+            if (!isLast) remaining -= shareCents;
+            return {
+              invoiceId: id,
+              staffId: s.staffId,
+              staffName: s.staffName,
+              sharePct: s.sharePct.toFixed(2),
+              shareCents,
+            };
+          });
+          await tx.insert(invoiceTipSplits).values(rows);
+        }
+      }
+
+      const [updatedInvoice] = await tx
         .update(invoices)
         .set(update)
         .where(eq(invoices.id, id))
         .returning();
 
-      // Atomically save tip splits when marking paid with provided splits
-      if (
-        body.status === "paid" &&
-        effectiveTipCents > 0 &&
-        incomingTipSplits !== undefined &&
-        incomingTipSplits.length > 0
-      ) {
-        await tx.delete(invoiceTipSplits).where(eq(invoiceTipSplits.invoiceId, id));
+      const lineItems = await tx
+        .select()
+        .from(invoiceLineItems)
+        .where(eq(invoiceLineItems.invoiceId, id));
 
-        let remaining = effectiveTipCents;
-        const rows = incomingTipSplits.map((s, i) => {
-          const isLast = i === incomingTipSplits.length - 1;
-          const shareCents = isLast ? remaining : Math.round((s.sharePct / 100) * effectiveTipCents);
-          if (!isLast) remaining -= shareCents;
-          return {
-            invoiceId: id,
-            staffId: s.staffId,
-            staffName: s.staffName,
-            sharePct: s.sharePct.toFixed(2),
-            shareCents,
-          };
-        });
-
-        await tx.insert(invoiceTipSplits).values(rows);
-      }
-
-      return [upd];
+      return [updatedInvoice, lineItems];
     });
 
-    const lineItems = await db
-      .select()
-      .from(invoiceLineItems)
-      .where(eq(invoiceLineItems.invoiceId, id));
-
     return c.json({ ...updated, lineItems });
   }
 );
diff --git a/apps/web/src/pages/Clients.tsx b/apps/web/src/pages/Clients.tsx
index 8f89d52..af4b47b 100644
--- a/apps/web/src/pages/Clients.tsx
+++ b/apps/web/src/pages/Clients.tsx
@@ -1,4 +1,4 @@
-import { useEffect, useState, useCallback, useRef } from "react";
+import { useEffect, useState, useCallback, useRef, useId } from "react";
 import { useSearchParams } from "react-router-dom";
 import type { Client, GroomingVisitLog, Pet } from "@groombook/types";
 import { PetPhotoDisplay } from "../components/PetPhotoDisplay.js";
@@ -647,8 +647,7 @@ export function ClientsPage() {
 
       {/* ── Client modal ── */}
       {showClientForm && (
-        <Modal onClose={() => setShowClientForm(false)}>
-          <h2 style={{ marginTop: 0 }}>{editingClient ? "Edit Client" : "New Client"}</h2>
+        <Modal title={editingClient ? "Edit Client" : "New Client"} onClose={() => setShowClientForm(false)}>
           <form onSubmit={submitClient}>
             <Field label="Full name">
               <input value={clientForm.name} onChange={(e) => setClientForm((f) => ({ ...f, name: e.target.value }))} required style={inputStyle} />
@@ -678,8 +677,7 @@ export function ClientsPage() {
 
       {/* ── Pet modal ── */}
       {showPetForm && (
-        <Modal onClose={() => setShowPetForm(false)}>
-          <h2 style={{ marginTop: 0 }}>{editingPet ? "Edit Pet" : "Add Pet"}</h2>
+        <Modal title={editingPet ? "Edit Pet" : "Add Pet"} onClose={() => setShowPetForm(false)}>
           <form onSubmit={submitPet}>
             <Field label="Pet name">
               <input value={petForm.name} onChange={(e) => setPetForm((f) => ({ ...f, name: e.target.value }))} required style={inputStyle} />
@@ -753,8 +751,7 @@ export function ClientsPage() {
 
       {/* ── Visit log modal ── */}
       {showLogForm && logPetId && (
-        <Modal onClose={() => setShowLogForm(false)}>
-          <h2 style={{ marginTop: 0 }}>Log Grooming Visit</h2>
+        <Modal title="Log Grooming Visit" onClose={() => setShowLogForm(false)}>
           {logsLoading[logPetId] && <p style={{ fontSize: 13, color: "#6b7280" }}>Loading history…</p>}
           {visitLogs[logPetId] && visitLogs[logPetId].length > 0 && (
             <div style={{ marginBottom: "1rem" }}>
@@ -817,8 +814,7 @@ export function ClientsPage() {
 
       {/* ── Delete confirmation modal ── */}
       {showDeleteConfirm && selectedClient && (
-        <Modal onClose={() => setShowDeleteConfirm(false)}>
-          <h2 style={{ marginTop: 0, color: "#dc2626" }}>Permanently Delete Client</h2>
+        <Modal title="Permanently Delete Client" titleStyle={{ color: "#dc2626" }} onClose={() => setShowDeleteConfirm(false)}>
           <p style={{ fontSize: 14, color: "#374151" }}>
             This will permanently delete <strong>{selectedClient.name}</strong> and all their pets. This action cannot be undone.
           </p>
@@ -856,7 +852,8 @@ export function ClientsPage() {
 
 // ─── Shared UI ───────────────────────────────────────────────────────────────
 
-function Modal({ children, onClose }: { children: React.ReactNode; onClose: () => void }) {
+function Modal({ children, onClose, title, titleStyle }: { children: React.ReactNode; onClose: () => void; title: string; titleStyle?: React.CSSProperties }) {
+  const titleId = useId();
   const modalRef = useRef<HTMLDivElement>(null);
 
   useEffect(() => {
@@ -898,15 +895,17 @@ function Modal({ children, onClose }: { children: React.ReactNode; onClose: () =
 
   return (
     <div
-      role="dialog"
-      aria-modal="true"
       style={{ position: "fixed", inset: 0, background: "rgba(0,0,0,0.45)", display: "flex", alignItems: "center", justifyContent: "center", zIndex: 100 }}
       onClick={(e) => { if (e.target === e.currentTarget) onClose(); }}
     >
       <div
         ref={modalRef}
+        role="dialog"
+        aria-modal="true"
+        aria-labelledby={titleId}
         style={{ background: "#fff", borderRadius: 8, padding: "1.5rem", maxWidth: 480, width: "calc(100% - 2rem)", maxHeight: "90vh", overflowY: "auto", boxShadow: "0 20px 60px rgba(0,0,0,0.3)" }}
       >
+        <h2 id={titleId} style={{ marginTop: 0, ...titleStyle }}>{title}</h2>
         {children}
       </div>
     </div>